Physical Review E最新文献

We investigate the location of the critical and tricritical points of the three-dimensional Blume-Capel model by analyzing the behavior of the first Lee-Yang zero, the density of partition function zeros, and higher-order cumulants of the magnetization. Our analysis is conducted through Monte-Carlo simulations, intentionally using only small system sizes. We demonstrate that this approach yields excellent results for studying the critical behavior of the model. Our findings indicate that, at the tricritical point, where logarithmic corrections are anticipated, the numerical results align closely with the theoretical exponents describing these corrections. These expected values are then employed to accurately determine the coordinates of the tricritical point. At the model's critical point, the corrections correspond to those of the three-dimensional Ising model criticality, which we also use to precisely ascertain the critical temperature at zero crystal field. Additionally, we utilize more traditional thermodynamic quantities to validate the self-consistency of our analysis.

We consider the random deposition of objects of variable width and height over a line. The successive additions of these structures create a random interface. We focus on the regime of heavy-tailed distributions of the structure width. When the structure center is chosen at random, the problem is exactly solvable, and the interface generically tends toward a self-affine random curve. The asymptotic behavior reached after a large number of iterations is universal in the sense that it depends on only three parameters: the shape of the added structure at its maximum, the power-law exponent of the width distribution, and the exponent that relates height and width. The parameter space displays several transitions that separate different asymptotic behaviors. In particular, for a set of parameters, the interface tends toward a fractional Brownian motion. Our results reveal the existence of a new class of random interfaces whose properties appear to be robust. The mechanism that generates correlations at large distances is identified, and it explains the appearance of such correlations in several situations of interest, such as the physics of earthquakes or the propagation of energy through a diffusive medium.

We explore the critical properties of the recently discovered finite-time dynamical phase transition in the nonequilibrium relaxation of Ising magnets after a temperature quench. The transition is characterized by a sudden switch in the relaxation dynamics and it occurs at a sharp critical time. While previous works have focused either on mean-field interactions or on investigating the critical time, we analyze the critical fluctuations at the phase transition in the nearest-neighbor Ising model on a square lattice using Monte Carlo simulations. By means of a finite-size scaling analysis, we extract the critical exponents for the transition. In two spatial dimensions, we find that the exponents are consistent with those of the two-dimensional Ising universality class when the system is initially in the vicinity of the critical point. For initial temperatures below the critical one, however, the critical exponents differ from the Ising-exponents, indicating a distinct dynamical critical phenomenon.

We study the effect of network topology on the collective dynamics of an oscillator ensemble. Specifically, we explore explosive synchronization in a system of interacting star networks. Explosive synchronization is characterized by an abrupt transition from an incoherent state to a coherent state. In this paper, we couple multiple star networks through their hubs and study the emergent dynamics as a function of coupling strength. The dynamics of each node satisfies the equation of a Kuramoto oscillator. We observe that for a small interstar coupling strength, the hysteresis width between the forward and backward transition point is minimal, which increases with an increase in the interstar coupling strength. This observation is independent of the size of the network. Further, we find that the backward transition point is independent of the number of stars coupled together and the interstar coupling strength, which is also verified using the Watanabe and Strogatz theory.

We describe a general procedure which allows to construct, given a family of Hamiltonians H([under q]̲,[under p]̲;[under λ]̲), a single new Hamiltonian H[over ̃]([under q]̲,[under p]̲) such that, on each level set of H[over ̃], the unparametrized orbits are those of a level set of H with the values of parameters [under λ]̲ varying with the value of H[over ̃]. The symmetry structure of H[over ̃] can be completely characterized, provided the symmetries of initial family are known. Our approach covers numerous models considered in literature as well as it allows to construct novel ones. It provides a far reaching generalization of the Hietarinta et al. coupling-constant metamorphosis method and another proof of the Darboux theorem.

An analytically solvable model of unsaturated lipid bilayer is derived by introducing finite bending angle of the unsaturated bond relative to straight part of the lipid chain considered previously in our model of semiflexible strings. It is found that the lateral pressure profile of unsaturated lipids has a distinct maximum in the unsaturated bond region due to the enhanced excluded volume effect caused by the bent bond, leading to an increase of entropic repulsion between the lipid chains. Simultaneously, just away from the unsaturated bond, some parts of the neighboring lipid chains have less probability to collide for geometrical reasons, causing depletion of entropic repulsion relative to the saturated lipid chains case and resulting in the local minima of the lateral pressure profile surrounding the maximum at the bent unsaturated bond. The lipid chain order parameter, the lateral pressure profile, and the area per lipid are computed for palmitoyl-oleoyl-phosphatidylcholine and compared with those for dipalmitoylphosphatidylcholine lipid bilayer.

Self-organized criticality is a dynamical system property where, without external tuning, a system naturally evolves towards its critical state, characterized by scale-invariant patterns and power-law distributions. In this paper, we explored a self-organized critical dynamic on the Sierpinski carpet lattice, a scale-invariant structure whose dimension is defined as a power law with a noninteger exponent, i.e., a fractal. To achieve this, we proposed an Ising-bond-correlated percolation model as the foundation for investigating critical dynamics. Within this framework, we outlined a feedback mechanism for critical self-organization and followed an algorithm for its numerical implementation. The results obtained from the algorithm demonstrated enhanced efficiency when driving the Sierpinski carpet towards critical self-organization compared to a two-dimensional lattice. This efficiency was attributed to the iterative construction of the lattice and the distribution of spins within it. The key outcome of our findings is a dependence of self-organized criticality on topology for this particular model, which may have several applications in fields regarding information transmission.

The inflation of an inner radial (or spherical) cavity in an amorphous solid confined in a disk (or a sphere) served as a fruitful case model for studying the effects of plastic deformations on the mechanical response. It was shown that when the field associated with Eshelby quadrupolar charges is nonuniform, the displacement field is riddled with dipole charges that screen elasticity, reminiscent of Debye monopoles screening in electrostatics. In this paper we look deeper into the screening phenomenon, taking into account the consequences of irreversibility that are associated with the breaking of Chiral symmetry. We consider the equations for the displacement field with the presence of "odd dipole screening," solve them analytically and compare with numerical simulations. Suggestions how to test the theory in experiments are provided.

We use Brownian dynamics simulations to study a model of a cyclic bacterial heat engine based on a harmonically confined colloidal probe particle in a bath formed by active Brownian particles. For intermediate activities, active noise experienced by large enough probes becomes Gaussian with exponential autocorrelation function. We show that, in this experimentally pertinent regime, the probability densities for stochastic work, heat, and efficiency are well represented by those of a single active Ornstein-Uhlenbeck particle (AOUP), effectively representing the whole many-body setup. Due to the probe's fast relaxation in the potential, in typical experimental implementations, good agreement can prevail even when the autocorrelation function of the active noise develops nonexponential tails. Our results show that the AOUP provides a convenient and accurate, analytically tractable effective model to mimic and analyze experimental bacterial heat engines, especially when operating with comparatively large probes and stiff traps.

We have studied the fluctuation (noise) in the position of sliding blocks under constant driving forces on different substrate surfaces. The experimental data are complemented by simulations using a simple spring-block model where the asperity contact regions are modeled by miniblocks connected to the big block by viscoelastic springs. The miniblocks experience forces that fluctuate randomly with the lateral position, simulating the interaction between asperities on the block and the substrate. The theoretical model provides displacement power spectra that agree well with the experimental results.